OBJECTIVE: To determine optimal particle size for a colloidal suspension to be used for increasing absorption coefficients of the liver and facilitate the detection of small hepatic metastases. METHODS USED: We have received from Polysciences, Inc., latex particle suspensions ranging in diameter from 0.5 to 5 microns. These are labeled with fluorescent dyes to enable quantitation of tissue distribution following intravenous injection of laboratory animals. We are currently experimenting with the extraction of these labeled latex particles from animal tissues for quantitative measurements. The extraction and exact quantitation of these particles presented unexpected difficulties and we are exploring alternate ways for this purpose. When these problems are solved, the optimal particle size for hepatic deposition will be determined. This will be followed by injection of biodegradable particles (contrast) which will be prepared and tested in animals seeking a suitable opaque agent for hepatic CT scanning. SIGNIFICANCE OF RESEARCH: We are trying to demonstrate that certain organs preferentially take up intravenously injected particles of specific diameters. This would prove to be a significant help in the development of an ideal intravenous contrast material for the opacification of the liver and spleen and may facilitate earlier detection of small liver metastases on computerized tomographic examinations of the liver and spleen.